Polycrystalline diamond (PCD) materials and PCD elements formed therefrom are well known in the art. Conventional PCD is formed subjecting diamond grains in the presence of a suitable solvent catalyst material to processing conditions of extremely high pressure/high temperature (HPHT), where the solvent catalyst material promotes desired intercrystalline diamond-to-diamond bonding between the grains, thereby forming a PCD structure. The resulting PCD structure produces enhanced properties of wear resistance and hardness, making such PCD materials extremely useful in aggressive wear and cutting applications where high levels of wear resistance and hardness are desired.
Solvent catalyst materials typically used for forming conventional PCD include metals from Group VIII of the Periodic table, with Cobalt (Co) being the most common. Conventional PCD can comprise from 85 to 95% by volume diamond and a remaining amount of the solvent catalyst material. The solvent catalyst material is present in the microstructure of the PCD material within interstitial regions that exist between the bonded-together diamond grains.
A problem known to exist with such conventional PCD is thermal degradation due to differential thermal expansion characteristics between the interstitial solvent catalyst material used to sinter the PCD and the intercrystalline bonded diamond. Such differential thermal expansion is known to occur at temperatures of about 400° C., causing ruptures to occur in the diamond-to-diamond bonding, and resulting in the formation of cracks and chips in the PCD structure.
Another problem known to exist with conventional PCD materials is also related to the presence of the solvent catalyst material used to sinter the PCD in the interstitial regions and the adherence of the solvent catalyst to the diamond crystals to cause another form of thermal degradation. Specifically, the solvent catalyst material is known to cause an undesired catalyzed phase transformation in diamond (converting it to carbon monoxide, carbon dioxide, or graphite) with increasing temperature, thereby limiting practical use of conventional PCD to about 750° C.
Attempts at addressing such unwanted forms of thermal degradation in PCD are known in the art. Generally, these attempts have involved forming a PCD body having an improved degree of thermal stability when compared to those conventional PCD materials discussed above. One known technique of producing a thermally stable PCD body involves at least a two-stage process of first forming a conventional sintered PCD body in the manner described above, and then removing the solvent catalyst material therefrom.
This method produces a diamond-bonded body that is substantially free of the solvent catalyst material, and is therefore promoted as providing a diamond-bonded body having improved thermal stability when compared to conventional PCD. However, the resulting thermally stable diamond-bonded body typically does not include a metallic substrate attached thereto, by solvent catalyst infiltration from such substrate due to the solvent catalyst removal process, as all of the solvent catalyst material has been removed therefrom.
Also, the resulting diamond body has a material microstructure comprising a matrix phase of bonded-together diamond grains, and a plurality of open interstitial regions, pores or voids distributed throughout the diamond body. The presence of such population of open voids throughout the diamond body adversely impacts desired mechanical properties of the diamond body, e.g., provides a diamond body having reduced properties of strength and toughness when compared to conventional PCD. It is theorized that the presence of the catalyst material within the voids in conventional PCD operates to place the surrounding diamond matrix in a state of compression that operates to provide improved mechanical strength, e.g., fracture toughness and/or impact strength, to the PCD. Removing the catalyst material from the diamond body is thus believed to remove the diamond from a compression state, thereby also reducing the above-noted related mechanical properties of the diamond body.
Thus, thermally stable diamond-bonded bodies made by removing the solvent catalyst material therefrom are known to be relatively brittle and have poor properties of strength and/or toughness, thereby limiting their use to less extreme or severe applications. This feature makes such conventional thermally stable diamond-bonded bodies generally unsuited for use in aggressive cutting and/or wear applications, such as use as a cutting element of a subterranean drilling and the like.
The resulting diamond-bonded body, rendered free of the solvent catalyst material, has a coefficient of thermal expansion that is sufficiently different from that of conventional substrate materials (such as WC—Co and the like) typically infiltrated or otherwise attached to conventional PCD bodies to provide a diamond-bonded compact to adopt the diamond-bonded body construction for use with desirable wear and/or cutting end use devices. This difference in thermal expansion between the now thermally stable diamond-bonded body and the substrate, combined with the poor wetability of the diamond-bonded body surface due to the removal of the solvent catalyst material, makes it very difficult to form an adequate attachment between the diamond-bonded body and conventionally used substrates, thereby requiring that the diamond-bonded body itself be attached or mounted directly to the wear and/or cutting device.
However, since such thermally stable diamond-bonded body is devoid of a metallic substrate, it cannot (e.g., when configured for use as a cutting element in a bit used for subterranean drilling) be attached to such drill bit by conventional brazing process. Thus, use of such thermally stable diamond-bonded body in this particular application necessitates that the diamond-bonded body itself be attached to the drill bit by mechanical or interference fit during manufacturing of the drill bit, which is labor intensive, time consuming, and which does not provide a most secure method of attachment.
Other attempts that have been made to improve the thermal stability of PCD materials include where the solvent metal catalyst material used to form the PCD is removed from only a region of the body, i.e., where the solvent metal catalyst is removed from a defined region of the diamond body that extends a depth from the body surface. Such diamond body constructions are formed by starting with conventional PCD, and then selectively removing the solvent metal catalyst from only a region of the body extending a depth from the body surface, wherein a remaining portion of the diamond body comprises conventional PCD. While this approach has demonstrated some improvement in thermal stability over conventional PCD, the resulting diamond body still suffers from the problems noted above. Namely, that the treated region rendered devoid of the catalyst material has reduced mechanical properties of strength and/or toughness when compared to conventional PCD, due to the absence of the catalyst material and the related presence of the plurality of empty pores or voids in the interstitial regions.
It is, therefore, desired that a diamond-bonded construction be developed having improved thermal characteristics and thermal stability when compared to conventional PCD materials. It is also desired that such diamond-bonded construction be engineered to include a suitable substrate to form a compact construction that can be attached to a desired wear and/or cutting device by conventional method such as welding or brazing and the like. It is further desired that such diamond-bonded construction display desired mechanical properties such as strength and toughness when compared to conventional thermally stable diamond-bonded bodies, i.e., characterized by having a plurality of empty interstitial regions fanned by removing the catalyst material therefrom.